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When a 3-
Place leads of continuity tester on the common (black) terminal and one of the traveler (brass or silver) terminals
Place leads of continuity tester on the common terminal and the other traveler terminal
Usually when a 3-
One of these switches will not turn the light on and off (while the light is on) and that is the bad switch.
Once you identify the bad switch, follow the steps below to verify it is bad and needs to be replaced.
Switches are spring loaded to minimize arching and prolong their life. However, a very small amount of arcing is present when a switch is toggled. A bad switch may not fail completely, burned contacts may cause intermittent failure. Keep this in mind when troubleshooting switches. Intermittent failure could make troubleshooting difficult, especially with 3 and 4-